Multi-metal fill with self-aligned patterning and dielectric with voids

ABSTRACT

Photolithography overlay errors are a source of patterning defects, which contribute to low wafer yield. An interconnect formation process that employs a patterning photolithography/etch process with self-aligned interconnects is disclosed herein. The interconnection formation process, among other things, improves a photolithography overlay (OVL) margin since alignment is accomplished on a wider pattern. In addition, the patterning photolithography/etch process supports multi-metal gap fill and low-k dielectric formation with voids.

BACKGROUND

Photolithography misalignment can be responsible for patterning defectsin Back End Of the Line (BEOL) metallization. Such patterning defects inBEOL can include line and vertical interconnect access (via)discontinuities, which can adversely impact product reliability andwafer yield.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with common practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of the variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a cross-sectional view of an exemplary structure in accordancewith some embodiments.

FIG. 2 shows a cross-sectional view of a structure after a layer ofphotoresist has been deposited and patterned, and an opening has beenetched in a dielectric stack through a self-aligned etching process inaccordance with some embodiments.

FIG. 3 shows a cross-sectional view of a structure after a conductivematerial fills openings in accordance with some embodiments.

FIG. 4 shows a cross-sectional view of a structure after a metal oxidelayer has been formed on conductive structures in accordance with someembodiments.

FIG. 5 shows a cross-sectional view of a structure after partial removalof patterns and a layer of photoresist has been deposited and patternedin accordance with some embodiments.

FIG. 6 shows a cross-sectional view of a structure after an opening hasbeen etched in a dielectric stack by a self-aligned etching process inaccordance with some embodiments.

FIG. 7 shows a cross-sectional view of a structure after a conductivematerial fills openings in accordance with some embodiments.

FIG. 8 shows a cross-sectional view of a structure after a metal oxidelayer has been formed on conductive structures in accordance with someembodiments.

FIG. 9 shows a cross-sectional view of a magnified portion of astructure after a metal oxide layer has been formed on conductivestructures in accordance with some embodiments.

FIG. 10 shows a cross-sectional view of a structure after a firstdielectric is disposed between and over the conductive structures, wherethe first dielectric features a void that is located between theconductive structures in accordance with some embodiments.

FIG. 11 a cross-sectional view of an exemplary interconnect structure inaccordance with some embodiments accordance with some embodiments.

FIG. 12 is a flow diagram of an exemplary patterning fabrication methodof multi-metal fill, self-aligned interconnects with dielectric linerlayer and dielectric layer cap in accordance with this disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over a second feature in the description that followsmay include embodiments in which the first and second features areformed in direct contact, and may also include embodiments in whichadditional features may be formed that are between the first and secondfeatures, such that the first and second features are not in directcontact. In addition, the present disclosure may repeat referencenumerals and/or letters in the various examples. This repetition doesnot in itself dictate a relationship between the various embodimentsand/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The term “nominal” as used herein refers to a desired, or target, valueof a characteristic or parameter for a component or a process operation,set during the design phase of a product or a process, together with arange of values above and/or below the desired value. The range ofvalues is typically due to slight variations in manufacturing processesor tolerances.

The term “vertical,” as used herein, means nominally perpendicular tothe surface of a substrate.

The chip fabrication process can divided into three “modules,” in whicheach module may include all or some of the following operations:patterning (e.g., photolithography and etch); implantation; metal anddielectric material deposition; wet or dry clean; and planarization(e.g., etch-back process or chemical mechanical planarization). Thethree modules can be categorized as front end of the line (FEOL), middleof the line (MOL)/middle end of the line (MEOL), and back end of theline (BEOL).

In FEOL, field effect transistors (FETs) are formed. For example, FEOLincludes the formation of source/drain terminals, a gate stack, andspacers on sides of the gate stack. The source/drain terminals can bedoped substrate regions formed with an implantation process after thegate stack formation. The gate stack includes a metal gate electrode,which can include two or more metal layers. The gate dielectric caninclude a high dielectric constant (high-k) material (e.g., greater than3.9, which is the dielectric constant of silicon oxide). Metals in thegate electrode set the work function of the gate, in which the workfunctions can be different between p-type FETs and n-type FETs. The gatedielectric provides electrical isolation between the metal gateelectrode and a channel formed between the source and the drainterminals when the FET is in operation.

In MOL, low level interconnects (contacts) are formed and can includetwo layers of contacts on top of each other. The MOL interconnects canhave smaller critical dimensions (CDs; e.g., line width) and are spacedcloser together compared to their BEOL counterparts. A purpose of theMOL contact layers is to electrically connect the FET terminals, i.e.,the source/drain and metal gate electrode, to higher level interconnectsin BEOL. A first layer of contacts in MOL, known as “trench silicide(TS),” are formed over the source and drain terminals on either side ofthe gate stack. In the TS configuration, the silicide is formed in thetrench and after the trench formation. The silicide lowers theresistance between the source and drain regions and the metal contacts.The gate stack and the first layer of contacts are considered to be onthe same “level.” The second layer of contacts are formed over the gateelectrode and TS. MOL contacts are embedded in a dielectric material, ora dielectric stack of materials, that ensures their electricalisolation.

In BEOL, an interlayer dielectric (ILD) is deposited over the MOLcontacts. The formation of high level interconnects in BEOL involvespatterning a hard mask (HM) layer and subsequently etching through theHM layer to form holes and trenches in the ILD. The ILD can be a low-kmaterial. Low-k materials can have a dielectric constant below 3.9,which is the dielectric constant of silicon oxide (SiO₂). Low-kmaterials in BEOL can reduce unwanted parasitic capacitances andminimize resistance-capacitance (RC) delays. BEOL interconnects includetwo types of conductive lines: the vertical interconnect access lines(vias) and the lateral lines (lines). The vias run through the ILD layerin the vertical direction and create electrical connections to layersabove or below the ILD layer. Lines are laid in the lateral directionwithin the ILD layer to connect a variety of components within the sameILD layer. BEOL includes multiple layers (e.g., up to 9 or more) of viasand lines with increasing CDs (e.g., line width) and line pitch. Eachlayer is required to align to the previous layer to ensure proper viaand line connectivity.

Line connectivity can be established through an alignment between thepattern on a photomask (reticle) and existing features on a wafersurface. This quality measure is known as “overlay (OVL) accuracy.”Alignment is critical because the reticle pattern must be preciselytransferred to the wafer from layer to layer. Since multiplephotolithography steps are used during patterning, any OVL misalignmentis additive and contributes to the total placement tolerances betweenthe different features formed on the wafer surface. The placementtolerances for each “photo-layer” are known as the “OVL budget.” Eachphoto-layer can have a different OVL budget depending on the incomingOVL misalignment, and the size/density of the features to be transferredon the wafer's surface. Since OVL misalignments are additive, they canadversely affect the OVL budget of each photo-layer.

The wafer and the reticle position data are measured with respect to acoordinate system defined for the exposure tool and are then used in aglobal or field-by-field manner to perform the alignment. Globalalignment, also known as “coarse alignment,” can use several marks toquickly align a wafer relative to the reticle. Field-by-field alignment,also known as “fine alignment,” can be used to align the reticle to eachexposure site. The fine alignment can compensate for non-uniformitiesobserved in the local topography, deposition non-uniformities, ordishing during chemical mechanical planarization (CMP) operations.

The use of a HM to form the interconnects in BEOL can have severallimitations. For example, the use of a HM can limit the photolithographyalignment window because the narrow patterned features present in the HMreduce the tolerance for misalignment errors. A reduction in alignmentwindow increases the risk for overlay errors, which in turn translatesto a higher probability of patterning defects on the wafer. Commonpatterning defects include metal bridges between vias and deformed viasor lines. Self-aligned interconnects can provide a relief to thephotolithography alignment requirements and increase the alignment, orOVL, window. This is helpful for high density areas of the chip wherethe line pitch is small.

Various embodiments in accordance with this disclosure provide BEOLinterconnect fabrication methods that employ a patterningphotolithography/etch process with self-aligned interconnects resultingin a wider pattern for OVL. This effectively increases the OVL marginand reduces the number of patterning defects. Furthermore, the processis simplified because an HM layer is no longer required. According tothis disclosure, the interconnect fabrication method supports the use ofa multi-metal gap fill process. The metal in the multi-metal gap fillprocess can be a conductive material such as, for example, graphene. Insome embodiments, the multi-metal gap fill interconnects are formedbefore the ILD layer. In some embodiments, the ILD layer is depositedsuch that it has naturally occurring voids to decrease the layer'sdielectric constant.

FIG. 1 is a cross sectional view of a structure 100 in accordance withsome embodiments. In some embodiments, structure 100 is a portion of asubstrate (not shown in FIG. 1) which includes at least one BEOLinterconnect network layer, in which vias and lines are formed. In someembodiments, the substrate can be a bare semiconductor wafer or apartially fabricated semiconductor wafer which includes previouslyformed layers. Structure 100 includes pattern structures 105, in whicheach pattern structure 105 includes a mandrel 110 (a center portion ofpattern structure 105), a first spacer 120, and a second spacer 122.First and second spacers 120 and 122 are disposed on opposing sidesurfaces of mandrel 110. In some embodiments, each mandrel 110 can bemade of amorphous silicon, silicon nitride or amorphous carbon. By wayof example and not limitation, the thickness of mandrel 110 can rangefrom 10 nm to about 100 nm. In some embodiments, spacers 120 and 122 canbe made of titanium oxide, titanium nitride, silicon oxide, or siliconnitride. The spacer thickness can range from 5 to 50 nm depending on thedesign. In some embodiments, mandrels 110 and spacers 120, 122 act as anetch mask, in which a width between two pattern structures 105 is shownas distance 125.

Mandrel 110 and spacers 120, 122 are disposed over an ILD layer 130. Byway of example and not limitation, ILD layer 130 has a thickness between10 and 100 nm. In some embodiments, ILD layer 130 can be a stack ofdielectrics such as, for example, a low-k dielectric and anotherdielectric: (i) a low-k dielectric (e.g., carbon doped silicon oxide)and a silicon carbide with nitrogen doping; (ii) a low-k dielectric anda silicon carbide with oxygen doping; (iii) a low-k dielectric withsilicon nitride; or (iv) a low-k dielectric with silicon oxide.

ILD layer 130 is disposed over an etch stop layer 140. In someembodiments, etch stop layer 140 has a thickness between 1 nm and 100nm. By way of example and not limitation, etch stop layer 140 is made ofsilicon carbide, silicon nitride, or silicon oxide. Structure 100 alsoincludes an underlying metal line 150. In some embodiments metal line150 can be part of an earlier metallization layer. Further, metal line150 is over an ILD layer 160 and etch stop layer 170.

A photolithography operation and a series of etch operations formopenings in dielectric layer 130 and etch stop layer 140. For example,in FIG. 2, a coat of photoresist 200 is photo-exposed and patterned overstructure 100 to create via opening 210 that has a width 220.Photoresist 200 can be used to expose areas of structure 100 where viaswill be formed and to protect other areas of structure 100 where viasshould not be formed. As shown in FIG. 2, the via and line opening widthcan be determined by distance 125. Hence, width 220 of opening 210 maybe wider than width 125. In some embodiments, opening 210 can be as wideas width 230. The scenario assumes that the OVL error in thephotolithography process is zero (no alignment error), and thereforewidth 220 shows no variation due to the photolithography process. Insome embodiments, the misalignment errors are nonzero and thereforewidth 220 of opening 210 can be wider than distance 125, but width 220cannot be wider than width 230 due to the variations in thephotolithography process. Therefore, the OVL error contributes to thelimit as to how close width 220 can be to width 230—which is the maximumwidth for opening 210 without any misalignment error. In someembodiments, the OVL window is considered to be at least wider thandistance 125.

An etch process removes exposed areas of ILD layer 130 and etch stoplayer 140 through photoresist via opening 210 to form an opening thatstops on underlying metal line 150. In some embodiments, the etchprocess has high selectivity for ILD layer 130 and etch stop layer 140.In some embodiments, the etch process automatically stops after apredetermined amount of time. An etch process which is terminated aftera predetermined amount of time is referred to as a “timed etch.” An“end-pointed” etch process is a process that automatically stops whenthe layer directly underneath the etched layer is detected; for example,when the underlying metal line 150 is detected. End-point detection ispossible because etch stop layer 140 and the underlying layer metal line150 are made of different materials. Consequently, they can havedifferent etch rates for a given etching chemistry. Detection of metalline 150 can be done through, for example, a change in the etch rate,which can be detected by in-situ metrology equipment such as, forexample, an optical emission microscope. Since the optical emissionmicroscope can be integrated into the etch chamber, the etch process canbe monitored in real-time. In some embodiments, the etch process may betimed for a first part of the process and end-pointed for a second partof the process. Since the etch process is required to etch differentmaterials (e.g., ILD layer 130 and etch stop layer 140), different etchchemistry may be required. An exemplary etch chemistry can include acombination of hydrobromic acid (HBr), helium (He), oxygen (O₂) andchlorine (Cl₂). In addition to the etch chemistry, other etch processparameters can be adjusted such as, for example, flow rate, temperature,and pressure. These parameters can be used to control the etch rate,etch profile, uniformity, etc. After formation of via opening 210,photoresist 200 is removed (i.e., stripped) and line openings 250 areexposed. In some embodiments, the height of via opening 210 is largerthan the height of line opening 250. In some embodiments, via and lineopenings 210 and 250 when filled with a conductive material formconductive structures in an interconnect layer.

FIG. 3 shows the structure of FIG. 2 after via opening 210 and lineopenings 250 are filled with a conductive material 300. In someembodiments, conductive material 300 is copper (Cu), cobalt (Co),aluminum (Al), graphene, or any other suitable conductive material.Conductive material 300 is polished by chemical mechanical polishing(CMP) to remove extra material (overburden) from the top of mandrels 110and spacers 120, 122.

Referring to FIG. 4, once conductive material 300 is polished, a topsurface of conductive material 300 is capped with an etch stop cappinglayer 400. In some embodiments, etch stop capping layer 400 can beselectively grown on conductive material 300. By way of example and notlimitation, etch stop capping layer 400 can be a metal oxide such as,for example, an Al-based, a Co-based, a tungsten (W)-based, a nickel(Ni)-based, or a zirconium (Zr)-based oxide. Those skilled in the artwill appreciate that these are merely examples and other appropriateoxides can be used. By way of example and not limitation, etch stopcapping layer 400 can be deposited with chemical vapor deposition (CVD),physical vapor deposition (PVD), or a spin-on process followed by ametal oxide patterning process. The role of etch stop capping layer 400is to protect conductive material 300 from subsequent etching processes.

In some embodiments, additional vias and lines can be formed by removingmandrels 110 to form a plurality of openings. Respective spacers 120 and122 associated with the mandrels 110 (to be removed) are not removed.Removal of mandrels 110 may not be global, e.g., across the wholestructure 100. For example, a patterned photoresist may be used toprotect areas of structure 100 where removal of mandrels 110 is notdesired. In some embodiments, a dry etch chemistry can be used to removemandrels 110. By way of example and not limitation, a dry etch chemistrycan be a combination of HBr, He, O₂, and Cl₂. After the mandrel removalprocess, a resist strip operation removes the photoresist. FIG. 5 showsthe structure of FIG. 4 after photoresist 500 is applied and patterned,and at least a portion of mandrels 110 are removed to form an opening510 between opposing first spacer 120 and second spacer 122.

In order to start the interconnect formation, a photoresist 600 isapplied on structure 100, and then patterned as shown in FIG. 6. At theend of the photoresist patterning process, via openings 610 are formedin photoresist 600. Some openings, like opening 510, are covered byphotoresist 600 so that they are not subjected to the etching process.During this process, the OVL window remains wide. For example, viaopening 610 has a width 630. In some embodiments, in which the OVL ormisalignment error is zero, via opening 610 may be as wide as width 620for at least two reasons: (i) because the via/line opening width isdefined by distance 640 between opposing spacers 120 and 122; and (ii)because metal oxide layer 400 protects conductive material 300 from theetching chemistry and therefore if width 630 is wider and includes anarea where conductive material 300 is exposed, the conductive materialis protected from etching. In some embodiments, the misalignment errorsare nonzero and therefore width 630 of via opening 610 can be wider thandistance 640, but cannot be wider than 620 due to variations in thephotolithography process. Hence, the OVL error limits how close width630 can be to width 620, which is a maximum width without anymisalignment errors. This is also true for via opening 610.

Referring to FIG. 6, exposed areas of ILD layer 130 and etch stop layer140 are etched through via openings 610 while covered areas of structure100 are protected from the etch process. A selective process removesexposed areas of layer 130 and layer 140 to form via openings in ILDlayer 130 and etch stop layer 140. In some embodiments, the etch processmay be timed, end-pointed, or a combination of the two. For example, theetch process can be timed for a first part of the process andend-pointed for a second part of the process. By way of example and notlimitation, the etch chemistry for the removal of ILD layer 130 may bedifferent than the etch chemistry for etch stop layer 140. In someembodiments, the etch processes are highly selective for ILD layer 130and etch stop layer 140. An exemplary dry etch chemistry is acombination of HBr, He, O₂, and Cl₂. Once the etch process is complete,patterned photoresist 600 is stripped and all openings, such as opening510, are exposed. In some embodiments, opening 510 is a line opening,and the height of via opening 610 is larger than the height of lineopening 510. In some embodiments, via and line openings 610 and 510 whenfilled with a conductive material form conductive structures in aninterconnect layer.

In FIG. 7, a conductive material 700 fills the formed via openings(e.g., via opening 610) and line openings (e.g., opening 510). In someembodiments, conductive material 700 is different than conductivematerial 300. In some embodiments, conductive material 700 can be Al,Co, Cu, graphene, or any suitable conductive material with appropriateresistivity.

In FIG. 8, excess conductive material 700 is polished with CMP down tothe level of metal oxide layer 400. In some embodiments, the excessconductive material 700 is etched with a metal etch process. In someembodiments, the excess conductive material 700 can be removed with acombination of CMP and dry etch. In the combination of CMP and dry etchcase, conductive material 700 can be recessed below the metal oxidelayer 400 level. Once conductive material 700 is polished, its topsurface is capped with an etch stop capping layer 800. In someembodiments, lines or vias with different conductive material 300 and700 are alternating and they may have different selectively grown etchstop capping layers. In some embodiments, similar to etch stop cappinglayer 400, etch stop capping layer 800 selectively grows on conductivematerial 700. By way of example and not limitation, etch stop cappinglayer 800 can be a metal oxide such as an Al-based, a Co-based, aW-based, a nickel Ni-based, or a Zr-based oxide. Those skilled in theart will appreciate that these are merely examples and other appropriateoxides can be used. By way of example and not limitation, etch stopcapping layer 400 can be deposited with CVD, PVD, or a spin-on processfollowed by a metal oxide patterning process.

FIG. 9 is a magnified view of section 810 of FIG. 8. A selective etchremoves the remaining first spacers 120 and second spacers 122 as wellas mandrels 110 to form openings that will be filled with a dielectricliner layer. In some embodiments, spacers 120 and 122 can be removedwith a dry etch process or a wet etch process. By way of example and notlimitation, a dry etch chemistry can be fluorine-based (C_(x)H_(y)F_(z))or chlorine-based (Cl₂, B_(x)Cl_(y)). An exemplary wet etch chemistrycan be hydrochloric acid, phosphoric acid, nitric acid and hydrogenperoxide chemistry. FIG. 10 shows FIG. 9 after the removal of remainingfirst spacers 120 and second spacers 122 as well as mandrel 110, and theformation of a dielectric liner layer 1000. Dielectric liner layer 1000covers the etch stop capping layers 800, 400 and partially fills thespace between the formed interconnects (line spacing) allowing for avoid 1010 to be formed between the interconnects. Void 1010 may bereferred to as an “air-gap.” In some embodiments, void 1010 contains agas. In some embodiments, void 1010 is nominally gas free. Voids canhave a dielectric constant of nearly 1, therefore increasing the size ofthe void can further lower the dielectric constant of dielectric linermaterial 1000. In some embodiments the dielectric constant of dielectricliner layer 1000 with voids present can range from 2 to 6. In someembodiments, dielectric liner layer 1000 is deposited using a chemicalvapor deposition (CVD) or an atomic layer deposition (ALD) process. Thedeposition process conditions and the line spacing between conductivematerials 700 and 300 can modulate the size of the void. For example,process conditions such as pressure and gas ratios can affect theconformality of the deposited film and allow the void to be formed. Insome embodiments, the line spacing can range from 5 to 20 nm. At thisline spacing range, the void forms naturally and can occupy from 30 to70% of the total volume between conductive materials 700 and 300. By wayof example and not limitation, dielectric liner layer 1000 can be SiO₂,SiN, or SiC and its thickness can range from 10 to 100 nm. Due to voids1010 present in dielectric liner layer 1000, dielectric liner layer 1000may not have the thermo-mechanical rigidity to sustain vibrations ormechanical/thermal stress from subsequent processing. In someembodiments, a dielectric liner layer cap is formed to protectdielectric liner layer 1000 from fracture and/or collapse.

Referring to FIG. 11, a dielectric layer cap 1100 is spin-coated ordeposited with CVD over dielectric liner layer 1000. In someembodiments, dielectric layer cap 1100 is a low-k layer that providesmechanical support to dielectric liner layer 1000. In some embodiments,the thickness of dielectric liner layer 1000 can range between 10 and100 nm. In some embodiments, the dielectric constant of dielectric linerlayer 1000 can range from 2 to 6.

Referring to FIG. 12, a flow diagram of an exemplary patterningfabrication process 1200 of multi-metal fill, self-aligned interconnectswith dielectric liner layer and dielectric layer cap in accordance withthis disclosure is shown. Other fabrication operations may be performedbetween the various operations of method 1200, and are omitted merelyfor clarity. The patterning fabrication process of multi-metal fill,self-aligned metal lines with dielectric liner layer and dielectriclayer cap is not limited to the exemplary fabrication process 1200.

Exemplary process 1200 starts with operation 1210, where a plurality ofpattern structures are formed over a substrate such as, for example, asshown in FIG. 1. By way of example and not limitation, the substrate maybe a partially fabricated wafer which includes previously formed layers.Each pattern includes a mandrel 110 (center portion) and a correspondingpair of opposing spacers 120 and 122. An exemplary substrate includes anILD layer 130, an etch stop layer 140, and an underlying metal line 150.Metal line 150 is over ILD layer 160 and etch stop layer 170 as shown inFIG. 1. Other layers may be present below etch stop layer 170 but arenot shown for clarity. In some embodiments, mandrel 110 is made ofamorphous Si. In some embodiments, first and second spacers 120 and 122respectively are made of titanium oxide or silicon nitride. In someembodiments, mandrel 110 and spacers 120, 122 act as an etch mask sothat formed vias and lines are self-aligned to second spacer 122 of afirst mandrel 110 and first spacer 120 of a neighboring second mandrel110. By way of example and not limitation, ILD layer 130 has a thicknessbetween 10 and 100 nm. In some embodiments, ILD layer 130 can be a stackof dielectrics such as a low-k dielectric and another dielectric: (i) alow-k dielectric (e.g., carbon doped silicon oxide) and a siliconcarbide with nitrogen doping; (ii) a low-k dielectric and a siliconcarbide with oxygen doping; (iii) a low-k dielectric with siliconnitride; or (iv) a low-k dielectric with silicon oxide.

Exemplary process 1200 continues with operation 1215, where firstopenings are formed in the substrate and are self-aligned to the patternstructures. Referring to FIG. 1, the opening includes via openings inILD layer 130 and etch stop layer 140. Vias electrically connect twolayers in the vertical direction, and lines make electrical connectionswithin the same layer in a plane that is substantially parallel to thesurface of the substrate. Operation 1215 involves severalphotolithography and etch operations. Referring to FIG. 2, a photoresistlayer 200 is coated, photo-exposed, and patterned over structure 100 tocreate opening 210 with width 220. A subsequent etch process removesexposed areas of ILD layer 130 and etch stop layer 140 throughphotoresist opening 210 to from a via opening that stops on underlyingmetal line 150. The etch process can have high selectivity for ILD layer130 and etch stop layer 140. An exemplary etch chemistry can include acombination of HBr, He, O₂, and Cl₂. In some embodiments, the etchprocess automatically stops after a predetermined amount of time. Insome embodiments, the etch process may be timed for a first part of theprocess and end-pointed for a second part of the process.

In operation 1220, a first conductive material is disposed in theopenings to form an interconnect layer that includes conductivestructures. The conductive material extends upwardly from the firstopening to substantially fill a region between the second spacer of afirst structure and the first spacer of a neighboring second structure.Referring to FIG. 3, conductive material 300 fills via openings 210(formed in previous operation 1215) and line openings 250. In someembodiments, the height of via opening 210 is larger than the height ofline opening 250. In some embodiments, via and line openings 210 and 250when filled with a conductive material form conductive structures in aninterconnect layer. In some embodiments, conductive material 300 is Cu,Co, Al, graphene, or any other suitable conductive material. Conductiveline 300 is then polished to the level of structure 110 and spacers120/122 with a CMP process.

After the CMP process, a metal oxide layer is selectively grown on theconductive structures. The metal oxide layer is an etch stop cappinglayer such as, for example, layer 400 in FIG. 4. By way of example andnot limitation, etch stop capping layer 400 can be a metal oxide such asan Al-based, a Co-based, a W-based, a Ni-based, or a Zr-based oxide.Those skilled in the art will appreciate that these are merely examplesand other appropriate oxides can be used. By way of example and notlimitation, etch stop capping layer 400 can be deposited with CVD, PVD,or a spin-on process followed by a metal oxide patterning process. Arole of etch stop capping layer 400, among others, is to protectconductive material 300 from subsequent etching processes.

In operation 1225, additional via openings and line openings are formedby removing a portion, or all, of mandrels 110, from the patternstructures in predetermined locations according to, for example, aninterconnect layout of the integrated circuit being manufactured.Photolithography may be used to define the areas of structure 100 wheremandrels 110 are to be removed. A selective etch process removes aportion of the mandrels 110 without removing its corresponding pair ofopposing first and second spacers 120 and 122, thus forming an opening(e.g., opening 510 shown in FIG. 5). In some embodiments, a dry etchchemistry can be used to remove mandrels 110. By way of example and notlimitation, a dry etch chemistry can be a combination of HBr, He, O₂,and Cl₂. After removal of mandrels 110, photoresist 500, which was usedin the photolithography process, is stripped.

In operation 1230, openings are formed that are self-aligned to theopposing first and second spacers (120 and 122) of the patternstructure. This operation involves similar photolithography and etchprocesses as described in connection with operation 1215. For example,referring to FIG. 6, photoresist 600 is applied on structure 100 andthen patterned. At the end of the photoresist patterning process, viaopenings 610 are formed in photoresist 600. Some openings, like opening510 between neighboring spacers 120, are covered by photoresist 600 sothat they are not exposed to the etching process.

During this process, the OVL window remains wide. For example, opening610 has a width 630. In some embodiments, in which the OVL ormisalignment error is zero, opening 610 may be as wide as width 620 forat least two reasons: (i) because the via/line opening width is definedby distance 640 between opposing spacers 120 and 122; and (ii) becausemetal oxide layer 400 protects conductive material 300 from the etchingchemistry and therefore if width 630 is wider and includes an area whereconductive material 300 is exposed, the conductive material is protectedfrom etching. In some embodiments, the misalignment errors are nonzeroand therefore width 630 of opening 610 can be wider than distance 640,but cannot be wider than 620 due to variations in the photolithographyprocess. Hence, the OVL error limits how close width 630 can be to width620, which is a maximum width without any misalignment errors. This isalso true for opening 610.

A selective process removes exposed areas of ILD layer 130 and etch stoplayer 140 through photoresist openings 610 to form a via opening thatstops on underlying metal layer 150. The photoresist is then stripped.By way of example and not limitation, etch chemistry for the removal ofILD layer 130 may be different than the etch chemistry for stop etchlayer 140. In some embodiments, the etch processes are highly selectivefor ILD layer 130 and etch stop layer 140. An exemplary etch chemistrycan include a combination of HBr, He, O₂, and Cl₂. In some embodiments,the etch process is timed, end-pointed, or a combination of the two. Forexample, an etch process is timed in the beginning of the process andend-pointed towards the end of the process.

In operation 1235, another conductive material fills the secondopening(s) to form an additional interconnect layer that includesconductive structures. In FIG. 7, a conductive material 700 fills viaopenings 610 and line openings 510. In some embodiments, opening 510 isa line opening, and the height of via opening 610 is larger than theheight of line opening 510. In some embodiments, via and line openings610 and 510 when filled with a conductive material form conductivestructures in an interconnect layer. In some embodiments, conductivematerial 700 is different than conductive material 300. In someembodiments, conductive material 700 is Al, Co, Cu, graphene, or anysuitable conductive material with appropriate resistivity. In FIG. 8,conductive material 700 is polished with CMP down to the level of metaloxide layer 400. In some embodiments, excess conductive material 700 isetched with a metal etch process. In some embodiments, the excessconductive material 700 can be removed with a combination of CMP and dryetch. In the CMP and dry etch case, conductive material can be recessedbelow the metal oxide layer 400. Once conductive material is polished oretched, its top surface is capped with an etch stop capping layer 800.In some embodiments, lines or vias with different conductive material300 and 700 are alternating. Conductive material 300 and 700 arealternating may have different selectively grown etch stop cappinglayers. In some embodiments, like etch stop capping layer 400, etch stopcapping layer 800 is selectively grown on conductive material 700. Byway of example and not limitation, etch stop capping layer 800 can be ametal oxide such as, for example, an Al-based, a Co-based, a W-based, anickel Ni-based, or a Zr-based oxide. Those skilled in the art willappreciate that these are merely examples and other appropriate oxidescan be used. By way of example and not limitation, etch stop cappinglayer 400 can be deposited with CVD, PVD, or a spin-on process followedby a metal oxide patterning process.

In step 1240 opening are formed by removing the opposing first andsecond spacers 120, 122 and the remaining mandrels 110 to form openingsto be filled with a dielectric liner layer. In some embodiments, spacers120, 122 can be removed with a dry etch process or a wet etch process.By way of example and not limitation, a dry etch chemistry can befluorine-based (C_(x)H_(y)F_(z)) or chlorine-based (Cl₂, B_(x)Cl_(y)).An exemplary wet etch chemistry can be hydrochloric acid, phosphoricacid, nitric acid, and hydrogen peroxide chemistry.

In step 1245, the openings are filled with a dielectric liner layerwhere voids are being formed between the conductive structures. Forexample, referring to FIG. 10, a dielectric liner layer 1000 covers theetch stop capping layers 800, 400 and partially fills the space betweenthe formed interconnects (conductive material 300 and 700) allowing fora void 1010 to be formed between the interconnects. Void 1010 may bereferred to as an “air-gap.” In some embodiments, void 1010 contains agas. In some embodiments, void 1010 is nominally gas free. Voids canhave a dielectric constant of nearly 1, therefore increasing the size ofthe void can further lower the dielectric constant of dielectric linermaterial 1000. In some embodiments, the dielectric constant ofdielectric liner layer 1000 with voids present can range from 2 to 6. Insome embodiments, dielectric liner layer 1000 is deposited using a CVDor an ALD process. The deposition process conditions and the size of theavailable space between the interconnects can modulate the size of thevoid. Process conditions such as pressure and gas ratios can affect theconformality of the deposited dielectric liner layer and allow the voidto be formed. In some embodiments, the line spacing can range from 5 to20 nm. At this line spacing range, the void forms naturally and canoccupy anywhere from 30 to 70% of the total volume between conductivematerials 700 and 300. Dielectric liner layer 1000 can be SiO₂, SiN, orSiC and its thickness can range from 10 to 100 nm. Due to voids 1010present in dielectric liner layer 1000, this layer does not have thethermo-mechanical rigidity to sustain vibrations or mechanical/thermalstress from subsequent processing. In some embodiments, a dielectricliner layer cap is used to protect dielectric liner layer 1000 fromfracture and/or collapse.

In step 1250, a dielectric cap layer is formed over the liner dielectriclayer. Referring to FIG. 11, a dielectric layer cap 1100 is spin-coatedor deposited with CVD over dielectric liner layer 1000. In someembodiments, dielectric layer cap 1100 is a low-k layer that providesmechanical support to dielectric liner layer 1000. In some embodiments,the thickness of dielectric liner layer 1000 is between 10 and 100 nmwith a dielectric constant between 2 and 6.

An interconnect formation process that employs a patterningphotolithography/etch process with self-aligned interconnects isdisclosed to improve the photolithography OVL margin since alignment isaccomplished on a wider pattern. A wider OVL window reduces waferdefectivity associated with patterning such as, for example, metalbridges and deformed interconnects.

Patterning defects are a reliability concern which adversely impactswafer yield. In addition, the patterning photolithography/etch processwith self-aligned interconnects supports the use of a multi-metal gapfill process where the interconnects can be filled with different typesof conductive material. The multi-metal gap-fill process utilizes aselective metal oxide that is grown after a fill process to protect adeposited metal from subsequent etch processes. In some embodiments,dielectric liner layer is formed between the interconnects. The linerdielectric layer includes voids, or “air-gaps”, in the space between theformed interconnects. The voids, or “air-gaps,” further lower thedielectric constant of the liner dielectric layer. A dielectric caplayer is formed over the dielectric liner layer to protect thedielectric liner layer from fracture and/or collapse.

In some embodiments, a semiconductor fabrication method includes asubstrate, a dielectric stack formed over the substrate. A firstinterconnect layer made of a first conductive material and a secondinterconnect layer made of a second conductive material formed on adielectric stack. The first and second conductive materials aredifferent from one another. A first metal oxide layer is formed on thefirst interconnect layer and a second metal oxide layer is formed on thesecond interconnect layer. A first dielectric layer which includes avoid is formed between the first and second interconnect layers and overthe first and second metal oxides layers. A second dielectric layer isformed over the first dielectric layer.

In some embodiments, a semiconductor fabrication method includes asubstrate and a dielectric stack formed over the substrate. A firstinterconnect layer and a second interconnect layer are formed with atleast one of the first and second interconnect layers disposed in thedielectric stack. An opening is formed between the first and secondinterconnect layers. A first dielectric layer that includes an openingis disposed in the opening. A second dielectric layer is formed over thefirst dielectric layer.

In some embodiments, a semiconductor device includes a substrate and adielectric stack over the substrate. A first dielectric layer over thedielectric stack and a second dielectric layer over the first dielectriclayer. A first conductive structure embedded in the first dielectriclayer, where the first conductive structure forms a first interconnectlayer with a first conductive material and a first portion thatpenetrates through the dielectric stack. A second conductive structureis embedded in the first dielectric layer, where the second conductivestructure forms a second interconnect layer with a second conductivematerial and a second portion that penetrates through the dielectricstack. The first dielectric layer includes a void formed between thefirst and second conductive structures.

It is to be appreciated that the Detailed Description section, and notthe Abstract of the Disclosure section, is intended to be used tointerpret the claims. The Abstract of the Disclosure section may setforth one or more but not all possible embodiments of the presentdisclosure as contemplated by the inventor(s), and thus, are notintended to limit the subjoined claims in any way.

The foregoing disclosure outlines features of several embodiments sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art will appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art will also realize that suchequivalent constructions do not depart from the spirit and scope of thepresent disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A semiconductor fabrication method comprising:providing a substrate; forming a dielectric stack over the substrate;forming a first interconnect layer made of a first conductive materialand a second interconnect layer made of a second conductive material onthe dielectric stack, wherein the first and second conductive materialsare different from one another; forming a first metal oxide layer on thefirst interconnect layer and a second metal oxide layer on the secondinterconnect layer; forming a first dielectric layer between the firstand second interconnect layers and over the first and second metaloxides layers, wherein the first dielectric layer comprises a void; andforming a second dielectric layer over the first dielectric layer. 2.The method of claim 1, further comprising: forming at least onetransistor with one or more contact metal layers over the substrate;forming another interconnect layer over the one or more contact metallayers; forming the dielectric stack over the another interconnectlayer.
 3. The method of claim 1, wherein the first and the secondinterconnect layers comprise lines.
 4. The method of claim 1, whereinthe forming the first and second interconnect layers comprises: forminga first pattern structure and a second pattern structure over thedielectric stack, wherein each of the first and second patternstructures comprises a first spacer, a second spacer, and a centerportion between the first and second spacers; and depositing the firstconductive material between the first and second pattern structures. 5.The method of claim 4, further comprising: removing the center portionof the second pattern structure between the first and second spacers;and depositing the second conductive material between the first andsecond spacer of the second pattern structure.
 6. The method of claim 1,wherein the first and second conductive materials comprise copper,cobalt, aluminum, or graphene.
 7. The method of claim 1, wherein themetal oxide material layer comprises aluminum-based oxides, orcobalt-based oxides.
 8. A semiconductor fabrication method comprising:providing a substrate; forming a dielectric stack over the substrate;forming a first interconnect layer and a second interconnect layer,wherein at least one of the first and second interconnect layers isdisposed in the dielectric stack; forming an opening between the firstand second interconnect layers; disposing a first dielectric layer inthe opening, wherein the first dielectric layer comprises a void; andforming a second dielectric layer over the first dielectric layer. 9.The method of claim 8, further comprising: forming at least onetransistor with one or more contact metal layers over the substrate;forming another interconnect layer over the one or more contact metallayers; forming the dielectric stack over the another interconnectlayer.
 10. The method of claim 8, wherein the forming the first andsecond conductive structures comprises first and the second interconnectlayers comprise vias.
 11. The method of claim 8, wherein the forming thefirst and second interconnect layers comprises: forming a first patternstructure and a second pattern structure over the dielectric stack,wherein each of the first and second pattern structures comprises afirst spacer, a second spacer, and a center portion between the firstand second spacers; forming a first opening in the dielectric stack,wherein the first opening self-aligns to a space between the first andsecond pattern structures; depositing a first conductive material in thefirst opening to form the first conductive structure; and forming ametal oxide layer on the first conductive structure.
 12. The method ofclaim 11, further comprising: removing the center portion of the secondpattern structure between the first and second spacers; and forming asecond opening in the dielectric stack, wherein the second openingself-aligns to the first and second spacer of the second patternstructure; and depositing a second conductive material in the secondopening to form the second conductive structure, wherein the secondconductive material is different from the first conductive material; andforming another metal oxide layer on the second conductive structure,wherein the another metal oxide layer is different from the metal oxidelayer on first conductive structure.
 13. The method of claim 12, whereinthe first and second conductive materials comprise copper, cobalt,aluminum, or graphene.
 14. The method of claim 12, wherein the first andsecond metal oxide layers comprise aluminum-based oxides or cobalt-basedoxides.
 15. A semiconductor device comprising: a substrate; a dielectricstack over the substrate; a first dielectric layer over the dielectricstack; a second dielectric layer over the first dielectric layer; afirst conductive structure embedded in the first dielectric layer,wherein the first conductive structure forms a first interconnect layerwith a first conductive material and a first portion that penetratesthrough the dielectric stack; and a second conductive structure embeddedin the first dielectric layer, wherein the second conductive structureforms a second interconnect layer with a second conductive material anda second portion that penetrates through the dielectric stack; whereinthe first dielectric layer comprises a void formed between the first andsecond conductive structures.
 16. The semiconductor device of claim 15,further comprising: at least one transistor with one or more contactmetal layers over the substrate; and another interconnect layer over theone or more contact metal layers, wherein the dielectric stack is overthe another interconnect layer.
 17. The semiconductor device of claim15, wherein at least one of the first portion of the first interconnectlayer and the second portion of the second interconnect layer comprisesa via.
 18. The semiconductor device of claim 15, wherein the firstconductive material is different from the second conductive material.19. The semiconductor device of claim 15, wherein the first and secondconductive materials of the first and second interconnect layerscomprise copper, cobalt, aluminum, or grapheme.
 20. The semiconductordevice of claim 15, wherein the first conductive structure of the firstinterconnect layer comprises a first metal oxide layer over the firstconductive material and the second conductive structure of the secondinterconnect layer comprises a second metal oxide layer over the secondconductive material.